Ricekiller, there is a real difference between compression
ratio and compression
pressure. A compression tester will tell you the pressure in the cylinders that is caused by compression. That is affected by a whole lot of things, including the outside air pressure, the speed the starter cranks, and so on.
The compression ratio is simply the ratio of (fixed volume + swept volume) to fixed volume in the cylinder and combustion chamber. This will not change unless you change the pistons, heads, bore, stroke, etc.
The spreadsheet does give you correct results for compression ratios--
if you feed it the correct numbers
for your engine. That means you have to measure a whole bunch of things pretty carefully, like the combustion chamber volume, the piston dish (or dome), the deck height, etc. Note that the spreadsheet doesn't say squat about PSI readings--because that is a different (though not completely unrelated) issue.
You can find the spreadsheet (there are actually several available on the Web) here on Pelican's "Tech Specs" page:
http://www.pelicanparts.com/914/technical_specs/914_compression_ratio.htm .
--DD